How to grow sweet potato

Pick a well-drained field where water soaks away and does not sit — sweet potato roots rot in wet ground.

The best soil is light, sandy to sandy-loam. Roots swell easily and pull out clean; heavy, sticky clay gives small, twisted roots.

Choose ground that did not grow sweet potato last season (or the one before). Old sweet-potato land is already stocked with the weevil and root worms.

Keep the new field well away from any old or still-standing sweet-potato patch — the weevil walks and the virus-carrying insects fly across from there.

Clear out any volunteer sweet-potato plants nearby (self-sprouted from last year's leftover roots) — they are a bridge that carries the weevil and virus into your new crop.

Take only the top of the vine — the last forearm's length (≈25–30 cm), about 3–4 leaf-joints from the growing tip. The virus builds up lower down the old vine, so the tips are the cleanest part.

Cut only from mother plants that look strong, dark-green and healthy. Never cut from a plant that is stunted, or whose leaves are mottled, puckered, yellow-veined or crinkled — those are the sick ones.

Before you cut, walk your seed-vine patch and mark the best plants — vigorous, heavy-vining, disease-free ones make the best mothers (this is called positive selection).

Take cuttings fresh, the day you plant, if you can. If you must hold them a day or two, stand them in a cool, shaded place out of the sun — wilted, sun-dried cuttings root poorly.

Where the dry season is long and the vines die back, carry a few clean roots through it buried in dry sand, and sprout them early for vines. This is the 'Triple S' method — Store in Sand and Sprout — and it gives you clean planting material ahead of the rains.

Make ridges or mounds about one metre apart (a long stride), running across the slope so they catch the rain and don't wash away.

Build each ridge loose and high — about shin-high (≈20–30 cm). High, loose ridges give bigger, better-shaped roots and keep them well covered from the weevil.

Spread well-rotted manure or compost along the ridge line and mix it into the ridge — aim for about 5–10 t/ha. That is a thin scatter, not a heap: roughly one full wheelbarrow-load (about 50 kg) worked in along every 50–90 long strides (≈50–90 m) of ridge. Spread it thin; never dump a whole barrow on one spot.

Use only dark, crumbly, well-rotted manure. On sandy soil that dries fast, a little extra helps the ridge hold water; on heavier soil it keeps the ridge open so roots can swell.

Work the basal fertiliser into the top of the ridge a few days before planting, so it sits where the young roots will find it. Your recommendation gives the amount for your field.

Favour a fertiliser that is high in potassium (K) and low in nitrogen — potassium fills the roots, nitrogen mostly grows vines.

No bought fertiliser? Clean wood ash is a good local source of potassium — scatter a few handfuls along each stride of ridge and mix it in.

Mix it into the soil, not left on top, and keep the ridge moist so the food is there when the roots begin to set (around 6–9 weeks).

Plant into moist soil — after a good planting rain, or, under irrigation, after wetting the ridge. Cuttings root fast in damp, warm soil.

Use tip cuttings about a forearm long (≈25–30 cm) with a few leaves at the top.

Bury the lower 2–4 leaf-joints (nodes) — about 5–10 cm of stem — laid slanting or flat along the ridge, leaving 2 or more leaves above the soil. Roots grow from every buried joint, so more buried joints means more roots.

Space plants about a foot-length apart (≈30 cm) along the ridge, with ridges about a metre apart (one long stride).

Firm the soil around each buried stem so it sits snug in moist earth. Loose cuttings dry out and fail.

Walk the field about once a week through the first month — cover the whole field in a big "W", not just the edge by the path.

Look for sick plants: stunted, with small, puckered, crinkled leaves, yellowing along the veins (vein-clearing), mottled light-and-dark, or oddly purple. That is SPVD.

Turn a few leaves over and look underneath for whitefly (tiny white flies that lift off in a little cloud when disturbed) and aphids (small soft insects clustered on the shoots) — their build-up is what spreads the virus.

Count the gaps — cuttings that wilted or failed to root — so you know where to gap-fill.

Mark any sick plant to pull out now (see the roguing task). If whitefly and aphid numbers are building, the virus can spread fast — rogue hard (pull out and destroy every sick plant) and keep new plantings well away from old fields.

As soon as a plant shows stunting, puckered or vein-cleared leaves, mottling or purpling, dig it out — root and all.

Carry it right out of the field and burn it or bury it deep. Never leave pulled plants lying on the ridge or the field edge.

Do this every week through the first month, whenever a new sick plant appears.

Never take cuttings from a plant that has shown these symptoms — not now, and not at harvest.

If sick plants keep appearing even after roguing → your planting material was infected. Mark this field's vines as unfit for seed and get clean, virus-tested cuttings for next season.

About 1–2 weeks after planting, walk the ridges and find the gaps where cuttings wilted, dried or failed to root.

Plant a fresh clean tip cutting into each gap, into moist soil, the same depth and way as before.

Do it while the soil is still moist and the crop is only a week or two old, so the new plants are not left behind.

Take the replacement cuttings from healthy mothers only — never fill a gap with a cutting off a sick plant, or you seed the virus back in.

Keep the ridge moist for the first 2 weeks while the cuttings root — push in a finger and water when the top few centimetres are dry.

Water gently every 5–7 days, more often in heat or on sandy soil that dries quickly.

Don't waterlog the ridge — cuttings sitting in soggy soil rot instead of rooting.

Ease off once the cuttings have taken and new leaves are growing — established vines are drought-hardy and need much less.

Walk the field in a "W" about once a week, checking the vines, the leaves and the base of the plants.

Weevil: look at the vine bases and stems for small, slender, long-snouted weevils and feeding scars, and for any cracks in the soil opening down toward the roots.

Leaf blight (Alternaria): look on the older, lower leaves for dark brown spots with rings inside them (like a target) and a yellow halo — worst after warm, humid, wet spells. Pick off the worst-spotted leaves and keep the canopy open so leaves dry quickly. If the spots keep spreading through the canopy despite this → spray a protectant fungicide (one that coats the leaf to shield it from new infection, such as mancozeb), as the label directs.

SPVD: keep pulling any plant that turns up stunted, mottled or vein-cleared (see the roguing task).

If you see soil cracks or the first weevils, hill up straight away to cover the roots — closing cracks is your main weevil defence.

Do the first weeding by about 2 weeks, while the weeds are small and the vines are still short.

Do the second weeding by about 4 weeks, and hill up the ridge at the same time (see the hilling task) — one pass does both jobs.

Hoe shallowly, and keep the hoe away from the plant bases — deep hoeing near the vines cuts the young feeding roots.

Once the vines meet and cover the ground, stop hoeing — the canopy now suppresses weeds, and walking in disturbs the roots.

Around the second weeding (~4 weeks), draw loose soil up over the ridge to cover the plant bases and close any cracks.

Look for the cracks that open along the top of the ridge as the soil dries and the roots swell — these are the weevil's doorways.

Re-cover every crack with soil; where you can, water the ridge afterwards to help the soil settle and close.

Keep the storage roots covered by soil at all times — any root shoulder poking into the air or a crack is an open invitation to the weevil.

In a dry spell, water every 7–12 days and don't let the growing vines wilt for more than a day — in normal rains you needn't water, as the vines cope on their own.

Aim for steady, even moisture rather than dry-then-flood; big swings crack the ridge and stress the plant.

A light watering also closes soil cracks — a bonus against the weevil in hot, dry weather.

Never waterlog — sweet potato roots rot in soggy ground.

In a hard, drawn-out dry spell now, water if you possibly can — the leaf canopy and the first root-set are being decided, so this is second only to root-bulking as the time water turns into yield.

Check the ridges every 1–2 weeks, and more often in hot, dry weather when the soil cracks most.

Look for cracks opening down to the roots, for root shoulders poking out, and for the small long-snouted weevils on the vines and soil.

Re-cover every crack with loose soil the moment you find it (see the re-hilling task).

Check any root you expose — a bitter smell, dark pin-holes or winding tunnels mean the weevil is in. Cull those roots; never store them.

If the weevil is building up → harvest promptly once the roots are mature, rather than leaving them in dry, cracked soil — and set pheromone traps if you can get them.

Every 2–3 weeks through bulking, walk the ridges and mound loose soil over any cracks and exposed roots.

Focus on dry spells — that is when the ridge cracks most and the weevil is most active.

Where you can, water lightly after re-hilling to help the soil settle and the cracks close.

Keep every storage root fully under soil right up to harvest.

Keep the soil evenly moist through root-set and early bulking (roughly 45–100 days) — this is when water pays back the most.

Water about every 7–10 days, more often in heat and on sandy soil.

Avoid the dry-then-flood pattern — steady moisture makes smooth roots; big swings crack the roots and crack the ridge.

Ease off near maturity so the roots firm up and their skins set for lifting and storage — but never let the crop bake bone-dry and crack open.

From about 80 days, gently dig up one or two hills from different parts of the field to check.

Look at the roots: they should be at a good eating size for your variety, with firm, set skin that does not rub off easily.

Cut a root across: on a mature root the milky sap beads up and dries quickly on the cut; on an immature root it stays wet and runny.

Watch the crop too — some yellowing of the older leaves is a sign the roots are finishing.

If the roots are still small and the sap stays wet and runny → they are not ready. Cover the test hills back up, wait 1–2 weeks, and dig-test again. But if the weevil is building or the soil is cracking badly, lift now anyway rather than lose roots.

Lift on a dry day, when the soil is neither dust-dry nor muddy — roots come out cleaner and bruise less.

Loosen the ridge with a hoe or fork from the side, well away from the crown, then lift the roots out by hand. Digging straight down spears and cuts them.

Handle roots gently — don't throw or heap them hard. Every bruise, cut and torn skin invites rot and the weevil.

Sort as you lift: sound, unbroken roots in one basket; damaged, cut, cracked and weevil-holed roots (bitter smell, pin-holes, tunnels) kept separate to eat first — never stored with the good ones.

Save clean tip vines from your best, healthiest plants for next season's cuttings, or keep a few sound clean roots to sprout in sand (Triple S).